Cathode ray tube dot matrix shifting



E. G. REESE, JR

CATHODE RAY TUBE DOT MATRIX SHIFTING- Dec. 24, 1968 2 sheets-sheet 1 Filed May 31, 1967 Q o ubu NM INVENTOR Edward G. Reese,Jr.

WITNESSES: BQMMQQQ Y E N m U, A

Dec. 24, 1968 E. s. REESE, JR 3,418,518

ICATHQDE RAY TUBE DOT MATRIX SHIFTTNG Flled May s1, 1967 I DOT MATRIX GE NEQATOR 2 Sheets-Sheet 2 48 DOT MATRIX GENE$ATOR MAIN MAIN 55 53 SWEEP SWEEP/ X 3. 60 Y POSITIVE sun-"r 4 POSITIVE SHIFT E, L J 56 DECODE NEGATIVE SHIFT) .\NEGATIVE SHIFT FIG 3 COMPUTER A} I v 5 FL T|ME- ELECTRONIC ELECTRONIC SWITCH SWITCH iv A United States Patent 3,418,518 CATHODE RAY TUBE DOT MATRIX SHIFTING Edward G. Reese, In, Mitford, N.H., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 31, 1967, Ser. No. 642,470 5 Claims. (Cl. 315-22) ABSTRACT OF THE DISCLOSURE First and second deflection generators position the cathode ray beam of a cathode ray tube at a plurality of dot positions forming an n x in matrix array with each dot position located at a normal row and column coordinate of the matrix. A shift circuit is provided and adds a predetermined positive or negative voltage to the deflection generator voltage to cause a shifting of the normal dot position, in accordance with a specific character to be displayed. By providing a shifting circuit for both the horizontal and vertical sweep a normal dot position may be shifted to eight other positions depending upon the combination of shift signals. The cathode ray beam is unblanked at certain dot positions in accordance with a character to be written, so that the character may be displayed on the cathode ray tube face.

BACKGROUND OF THE INVENTION Field of the invention.-The invention relates to a cathode ray tube display system, and in particular, to a read-out display where various characters including letters, symbols, numerals, punctuation marks etc. are written on the face of a cathode ray tube for visual or photographic inspection.

Description of the prior art.-Various methods are employed to display characters on the face of a cathode ray tube and one of the most basic methods is the dot matrix method. In the dot matrix method a stepping waveform positions the cathode ray beam in a rectangular dot position array and the cathode ray beam is unblanked at each dot position forming the character to be written, so that the cathode ray tube face will light up in a plurality of tiny areas, thus forming the character.

Generation of extremely high quality characters depends upon the number of dot positions generated. With fewer dot positions there is an inferior diagonal quality in such letters as A, K, M, N, R, V, W, X, Y and Z. In fact, in many displays there is only one dot position to represent the entire diagonal line. In other instances rounding off of certain letters such as B, C, D, G, J, O, P, Q and U is desired.

A problem arises however in that to generate enough dot positions for a high quality array, proportionally more decoding circuits are needed thereby increasing cost and complexity. In addition to the increase in the decoding circuits, the unblanking circuits increase in complexity and there is a proportional increase in memory requirements.

If enough dot positions are generated, then the beam energy requirements of the cathode ray tube increase with writing speed.

A general object of this invention is to provide a high quality character display which obviates the need for the additional circuitry as required in the prior art.

SUMMARY OF THE INVENTION There is described a character display apparatus for a cathode ray tube system which includes a first deflection means for positioning the cathode ray beam of the cathode ray tube horizontally in a plurality of successive dot positions in accordance with a deflection waveform.

A second deflection means is provided for positioning the cathode ray beam vertically in a plurality of successive dot positions. Circuit means are provided for modifying at least one of the waveforms provided by the first or second deflection means such that the cathode ray beam may be positioned intermediate the normal dot positions, as dictated by the specific character to be displayed on the cathode ray tube face. The specific character to be displayed also governs an unblanking circuit means which causes the cathode ray beam to turn on at specific ones of the dot positions.

For more than one character to be displayed, a main horizontal and vertical sweep generator means may be provided to position each complete set of dot positions generated by the first and second deflection means.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a typical dot position matrix for displaying a character;

FIG. 2 illustrates the dot matrix of FIG. 1 displaying the character N;

FIG. 3 is a block diagram illustrating an embodiment of the present invention;

FIG. 4 illustrates various waveforms at certain points in the circuit of FIG. 3; and

FIG. 5 illustrates the shift circuit portion of FIG. 3 in somewhat more detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1 there is illustrated a 5 x 7 dot matrix array wherein each of the 35 dot positions have been given a respective number 1 through 35. Each dot position represents a point on a cathode ray tube face where the cathode ray beam would strike (if it were turned on) as the beam is deflected horizontally and vertically by deflection circuitry. Travel of the cathode ray beam in a horizontal direction is a scan along the X axis whereas movement of the beam vertically represents a scan along the Y axis.

Normally, the deflection circuitry provides voltage waveforms which would position the cathode ray beam at dot position 1 and thereafter at the next successive dot position 2 and thereafter at the next successive dot position 3, etc. The present invention includes shifting means whereby the normal dot position may be shifted to a point intermediate normal dot positions. By way of example, consider dot position 18, a positive shift along the X axis will move dot position 18 to dot position 18E whereas a negative shift along the X axis will position it to a point designated 18W. Similarly, a positive shift along the Y axis will move dot position 18 to 18N whereas a negative shift will move it to 185. By combinations of a positive and negative shifting along the X and Y axis, dot position 18 may also be moved to positions ISNE, E, 188W and 18NW.

One method of shifting a normal dot position would be to provide an analog voltage proportional to a desired variable shift distance. However this would require a somewhat complex analog deflection circuit. As an alternative a dot position may be shifted by a predetermined and fixed amount upon the occurrence of a shift signal. For most applications this would result in a high quality character display. By way of example, if the distance between successive dot positions is D then a normal dot position may be caused to move /3 D. In FIGURE 1 therefore and considering the distance between dot positions 18 and 17, the cathode ray beam may strike the cathode ray tube face at any one of four points, that is, dot position 18, dot position 18E, dot position 17, and dot position 17W. With both vertical and. horizontal shifting a total of 9 different dot positions is possible; considering 2 normal dot positions, such as 17 and 18 therefore, a total of 18 different dot positions is possible.

The provision of shifting a dot position to a point M; the distance between normally successive dot positions results in a capability to display high quality characters. In FIG- URE 2 there is illustrated a character, the letter N, displayed on a 5 x 7 matrix such as illustrated in FIGURE 1.

When the scanning is such that the cathode ray beam would be at dot position 1 the beam is unblanked, that is the beam is turned on such that the beam strikes the cathode ray tube phosphor and dot position 1 is caused to glow. The Scanning proceeds until dot position 5 whereupon the cathode ray beam is unblanked to cause excitation of the cathode ray tube phosphor. The beam is then deflected in a Y direction to dot position 6 where it is unblanked and then scanned from right to left until dot position 9 at which time a negative shift is provided such that the cathode ray beam strikes the cathode ray tube face at dot position 9W after unblanking. The cathode ray beam is unblanked at subsequent dot positions indicated, including dot positon 12E shifted positively from dot position 12, dot position 24W shifted negatively from dot position 24 and dot position 27E shifted positively from dot position 27 to thereby provide four extra lighted areas in the diagonal of the character N instead of just one lighted area, that is dot position 18.

In FIGURE 3 there is illustrated apparatus for displaying high quality characters on a face of a cathode ray tube in accordance with the present invention. Letter designations in FIGURE 3 refer to corresponding waveforms of FIGURE 4. The apparatus includes a cathode ray tube unit 37 including a cathode ray tube 38 the face of which is illustrated and upon which is displayed a plurality of characters 40.

In order to position the cathode ray beam horizontally in a plurality of successive dot positions for displaying a single character, there is provided a first deflection means in the form of dot matrix generator 42 which is operable to provide a staircase waveform illustrated as solid curve a of FIGURE 4. Each voltage plateau represents a specific X coordinate for the cathode ray beam and each plateau has been given the number corresponding to the respective dot position such as illustrated in FIGURE 1. In other words, a deflection waveform provided by the dot matrix generator 42 having a magnitude of level 1 will position the cathode ray beam at dot position 1; with a voltage level at plateau 2 the cathode ray beam will be poistioned at dot position 2, etc. With the waveform a, the cathode ray beam sweeps (facing the tube 38) from left to right for the first row, from right to left for the second row, from left to right for the third row, etc., although, obviously other deflection waveforms could be provided for positioning the cathode ray beam horizontally in a plurality of successive dot positions. In an analogous manner, second deflection means for positioning the cathode ray beam vertically in a plurality of successive dot positions are provided and takes the form of the dot matrix generator 48 which provides the staircase waveform b illustrated in FIGURE 4 with the first plateau designated 1-5 maintaining the first 5 dot positions in a first row, the second plateau designated 6-10 maintaining the next 5 dot positions in a second row, the next plateau labelled 11-15 maintaining the next 5 dot positions in a third row etc. The combination of waveforms a and b therefore applied to the deflection circuitry of the cathode ray tube is operable to provide the dot position matrix of FIGURE 1.

Dot matrix generators such as 42 and 48 for generating staircase waveforms are well known to those skilled in the art. Having the capabilities of providing a dot position matrix, means are generally provided for unblanking, that is turning on the cathode ray beam at specific dot positions in accordance with characters to be written. Generally in such display systems an instruction to display a certain character or characters may emanate from a character generator or more often, from a computer. The instruction so provided is received by some sort of decoding network which may include various memory and decoding circuits which then provide the necessary timing and unblanking signals for a proper display of the character. In the present invention not only are the unblanking signals provided for character display but means are additionally provided for modifying at least one of the waveforms of the dot matrix generators for positioning the cathode ray beam to a point intermediate the normal successive dot positions as dictated by specific characters to be displayed. In FIGURE 3 provision is made for modifying the output of generators 42 and 48 by means of shift circuitry 50 and 51 respectively. Each of the shift circuits 50 and 51 receive respective positive and negative shift signals on lines 53 and 56 from the decode network 60 which is operable not only to provide the shift signals but to provide an unblanking signal to the unblanking amplifier 62 for turning on the cathode ray beam. The decode network 60 may provide respective shift and unblanking signals in response to an instruction from computer 64 or alternatively the decode circuit 60 could be an integral part of the computer 64.

The output of the shift circuit 50 is a positive or negative voltage on line 67 and is combined with the output of the matrix generator 42 in the summing circuit 69, the output of which is eventually fed to the deflection amplifier 72 for sweeping the cathode ray beam in the X direc tion. Similarly, when the shift circuit 51 receives a positive or negative shift input signal, a positive or negative voltage of a predetermined value is provided on output line 74 and is combined with the output of the matrix generator 48 in summing circuit 75. The deflecton amplifier 78 is responsive to the output of the summing circuit for controlling the cathode ray beam in the Y direction.

The apparatus thus far described is operable to provide positioning voltages for a cathode ray beam for the display of a single character. In the majority of instances it is desired to display a plurality of characters so that a meaningful message maybe visualized. Accordingly, there is provided deflection means in the form of main sweep deflection circuit 81 for the X axis sweep and main sweep circuit 82 for the Y axis sweep, the outputs of which are combined in summing circuits 84 and 85 with the outputs of summing circuits 69 and 75, respectively. The main sweep deflection waveforms therefore when combined with the dot matrix generator waveforms have the effect of providing a plurality of rows of dot matrices each matrix having the form as in FIGURE 1. In other operations, the main sweep deflections may be governed by a decoded computer instruction so that a character may be displayed anywhere on the face of the cathode ray tube such as in aircraft identification and control situations.

Waveforms c and d of FIGURE 4 illustrate the necessary signals provided by the decode circuit 60 for displaying the character N as illustrated in FIGURE 2. With reference therefore to FIGURES 2, 3 and 4, waveform c appears on output line 88 of the decode circuit 60 and comprises a plurality of precisely timed pulses. For ease of understanding each pulse has been given the number corresponding to the dot position where the pulse occurs for displaying the character N. By way of example, in the first row the cathode ray beam is unblanked at dot positrons 1 and 5. The first unblanking signal of waveform c is labelled 1 and occurs at the same time that waveform a is at the first plateau. The next unblanking signal labelled 5 occurs when the waveform a is at the plateau labelled 5. After plateau 5 has been reached waveform b drops down to plateau 6-10 for writing in the second row of the dot matrix. The third unblanking signal labelled 6 occurs when waveform a is at plateau 6 and the next unblanking signal occurs at dot position 9. At dot position 9 however, the decode circuit in accordance with the present invention receives on line 54 a negative shift signal and the shift circuit 50 provides a negative pulse labelled 9 in waveform d to modify waveform a. This modification shows up as a decrease in voltage of plateau 9, the de crease being illustrated in dotted lines labelled 9W and being equal to /3 the difference in voltage between plateaus 9 and 10 since, it will be remembered, in the embodiment of the present example the dot position is operable to move /3 the distance between normal successive dot positions. The normal unblanking sequence continues up until dot position 12 at which time the decode circuit provides a positive shift signal on output lead 53 to the shift circuit 50 which then provides an output signal labelled 12 in waveform d serving to modify the deflection waveform a. This modification shows up as a /3 increase in voltage and is represented by the dotted plateau designated 12E.

This general sequence is continued until the entire character is displayed. Since the character N does not require any vertical or diagonal shifts, waveform e representing the output of shift circuit 51 does not provide any modifying voltages to the output of dot matrix generator 48 although for those characters which require a vertical or diagonal shift, waveform b is modified by such pulses as was waveform a by the output of shift circuit 50.

With respect to the pulses of waveform c it is to be noted that the pulses do not commence when waveform a changes to a next plateau, but occur at a time after the plateau has been reached. This is to ensure that all transients have decayed and then when unblanking occurs the cathode ray beam will strike the cathode ray tube face at exactly the required dot position. That is, by giving waveform a time to settle to the respective plateaus, accurate positioning of the cathode ray beam may take place.

To perform the function of shift circuits S or 51 any one of a variety of circuits may be utilized, one such illustrative arrangement being shown in FIGURE which additionally shows one type of summing circuit in somewhat more detail. The shift circuit 50 includes electronic switches 90 and 91 connected respectively to positive potential +V and to negative potential V. The electronic switches 90 and 91 are normally in an OFF condition such that neither of the voltages +V or -V appears at circuit point 92. Upon the application of a positive shift signal on lead 53 from the decode circuit 60, electronic switch 90 will close thereby applying the +V voltage through resistor 96 to circuit point 92. Similarly, if a negative shift voltage is provided on line 54, the electronic switch 91 Will close, applying the voltage V through resistor 97 to the circuit point 92.

The output of dot matrix generator 42 is applied through resistor 99 to circuit point 92 which forms the input to summing amplifier means 101. Since the output of summing amplifier means 101 is the inversion of the input signal, there is provided an inverting amplifier 103 the output of which constitutes the output signal of the summing circuit 69.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made by way of example. The provision of shifting voltages for certain characters to be displayed in combination with a dot position matrix generation means may be accomplished with various other types of circuitry. In addition, the principles applicable to shifting various dot positions may be applied to the main X and Y sweeps for variably positioning each 6 character from a normal character position on the tube face. Other modifications and variations of the present invention are made possible in the light of the above teachings.

I claim as my invention:

1. Display apparatus for displaying characters on the face of a cathode ray tube comprising:

(A) first deflection means for providing a first deflection waveform for positioning the cathode ray beam horizontally at a plurality of successive normal dot positions;

(B) second deflection means for providing a second deflection waveform for positioning the cathode ray beam vertically at a plurality of successive normal dot positions;

(C) shift circuit means for modifying at least one of said waveforms for positioning the cathode ray beam to a position intermediate normal successive dot positions in accordance with specific characters to be displayed; and

(D) unblanking circuit means for causing the cathode ray beam to turn on at certain ones of said positions in accordance with specific characters to be displayed.

2. Apparatus according to claim 1 wherein:

(A) the shift circuit means is operable to supply positive and/or negative voltages during the course of a character displayed; and which includes (B) signal combining means for combining at least one of the deflection waveforms with said positive and/ or negative voltages.

3. Apparatus according to claim 1 wherein:

(A) the distance between successive normal dot positions is D; and

(B) the shift circuit means is operable to shift the normal dot position by 1 /3 D.

4. Apparatus according to claim 1 wherein:

(A) the first deflection means includes a first staircase waveform generator;

(B) the second deflection means includes a second staircase waveform generator; and which includes (C) decode circuit means for providing output signals in accordance with particular characters to be displayed;

(D) a first shift circuit means responsive to the output of said decode circuit means for changing the level of particular steps in said first staircase waveform, and

(E) a second shift circuit means responsive to the output of said decode circuit means for changing the level of particular steps in said second staircase waveform.

5. Apparatus according to claim 1 which additionally includes:

(A) main horizontal and vertical sweep generator means for positioning each set of dot positions provided by the first and second deflection means.

References Cited UNITED STATES PATENTS 3,090,041 5/1963 Dell 340324 RODNEY D. BENNETT, Primary Examiner.

T. H. TUBBESING, Assistant Examiner.

U.S. Cl. X.R. 3l524; 340-324 

